1. Field of the Invention
The present invention relates to a method and apparatus for forming an off-shore ice island structure, and more particularly for forming such an ice island structure in open waters.
2. Description of the Prior Art
In my U.S. Pat. No. 3,738,114, entitled "Method and Apparatus for Forming Ice Island for Drilling or the Like", issued June 12, 1973, a method and apparatus is disclosd for forming an ice island on natural ice in cold regions such as the north slope of Alaska. The present method and apparatus is similar in many respects to that disclosed in the above-identified patent, except that, as will be seen, the present method and apparatus can be utilized to form an ice island structure in open waters. There is no need to wait for sea water to freeze to a depth sufficient to support the weight of construction equipment and wall structures. Instead, the first part of the winter can be used to build up the ice island height.
As described in more detail in the patent, recovery of underwater resources such as oil from off-shore areas in Arctic an Antarctic regions is extremely difficult, particularly since areas such as the north slope of Alaska are covered with ice during most of the year.
Conventional steel platforms fixed to the marine bottom provide satisfactory structure for drilling and related oil field operations, but such a structure must necessarily be very large and ponderous to resist the forces of shifting pack ice. This is also true of artificial islands made of earth or other fill material where such material is available. In addition, such structures are permanent and cannot be moved to new drill sites once drilling is completed at the first site. There are also environmental concerns, a large platform or earth island being a permanent disruption of the native environment.
U.S. Pat. No. 3,750,412, issued Aug. 7, 1973, and U.S. Pat. No. 4,094,149, issued June 13, 1978, disclose artificial ice islands constructed on natural ice. Such islands are environmentally less objectional compared to earth islands, but they are incapable of construction in open waters. Consequently, the initial winter season cannot be utilized to build up the ice mass of the island. Instead, the water must first be allowed to freeze to sufficient thickness, or a large ice floe must be towed to the drilling site from somewhere else. In addition to these shortcomings, the islands are incapable of movement to another drill site after they are completed. The cost of constructing such a permanent artificial island at each drill site is prohibitively expensive.